The hormonal milieu in early stages of bone cell differentiation modifies the subsequent sex-specific responsiveness of the developing bone to gonadal steroids

We have established previously that rat bone tissue, as well as rat and hum an-derived bone cells in culture, show a sex-specific response to gonadal s teroids in stimulation of the specific activity of the BE isozyme of creati ne kinase (CK) and DNA synthesis. This response could be modified by manipu lation of the endocrine environment during early stages in rat development. To further examine the influence of changing hormonal steroid milieu and v itamin D status on the action of gonadal steroids in developing bone tissue , we used two models of ectopic bone formation: demineralized tooth matrix (DTM) implanted under the skin, and femoral bone marrow (BM) transplanted u nder the kidney capsule of a syngeneic recipient mouse. The response to gon adal steroids in ossicles developed from implanted DTM depended on the reci pient's gender; injection of estradiol 17 beta (E-2; 5 mug) into young fema le mice 21 days after DTM implantation increased, 24 h later, CK activity i n the newly formed ossicles by similar to 60%, whereas injection of dihydro testosterone (DHT; 50 mug) had no effect on CK activity. In contrast, in ma le mice, DHT but not E, increased CK activity in the ossicles by similar to 50%. This sex-specific response was abolished in gonadectomized mice resul ting in a similar response of the ossicles to both E, and DHT. When DTM was implanted into vitamin D-deficient female mice, there was a lower basal CK activity and a significantly diminished response to E, in the newly formed bone tissues. When BR;I, which contains mesenchymal and stromal cells and committed osteoprogenitor cells, was transplanted into 6-week-old intact or gonadectomized female or male mice, the response of the newly formed bone ossicles, 21 days after transplantation, to E, or to DHT was according to t he gender of the donor. Bone formed from BR-I obtained from female mice res ponded to E, only and those formed from male BM responded to DHT only. Ossi cles developed from BM obtained from gonadectomized mice showed lack of res ponse to either gonadal steroid. Furthermore, only similar to 25% of the BM transplants obtained from castrated (CAST) male donors developed into ossi cles. Ossicles formed from Bh I obtained from vitamin D-deficient female do nors showed lack of response to gonadal steroids. These findings suggest th at the manipulation of the hormonal milieu in early stages of the different iation sequence of bone cells modifies the subsequent selective responsiven ess of the developing bone tissue to gonadal steroids.